1. Field of the Invention
This invention relates to the field of radio receiver and transmitter calibration and testing equipment and, more particularly, to an apparatus and method suitable for the calibration and testing of low-power, low-band radio frequency radio receivers and transmitters of the type used for detecting buried or hidden metal objects.
2. Description of the Prior Art
It has been customary in the past to use complex and expensive laboratory type equipment such as digital frequency counters, R.F. watt meters, signal generators, calibrated attenuators and the like for the purpose of calibrating and testing metal detection equipment of the type employing a transmitter alone or a receiver and a transmitter. This equipment is normally expensive, bulky and difficult for the unskilled to meaningfully utilize. Therefore, when such metal detection apparatus has failed to function correctly in the field as determined by the operator attempting to locate hidden or buried metal objects; it has heretofore been necessary for the operator to take the malfunctioning equipment to a trained technician in order to determine which unit was defective, if any, or to have either the receiver or the transmitter or both recalibrated.
In a commercial setting, where the operator might be a utility company worker attempting to locate buried pipes, cables and so forth, the operator's time lost due to the suspected malfunction would not only give rise to a non-productive overhead expense, but it would also mean that the task to have been performed by the operator would have been postponed for some time. The operator would have to return to his dispatch point, obtain substitute equipment and return to the job site. Assuming the substitute equipment was properly functioning, only then could he perform the task at hand. If there had been any urgency attached to that task, the time delay could have had serious consequences.
If the object sought to be located by the utility company had been a pipe suspected to be leaking gas, the gas leak could continue for quite some time unabated while substitute equipment was being brought to the site. Alternatively, if it is not realized that the metal detecting equipment is not operating properly, the operator might fail to detect the presence of a buried pipe or cable, commence digging under the misconception that it was safe to do so, and rupture a gas main, destroy utilities cables, or cause other undesirable results. Thus, it is important that there be a simple to operate, in-the-field test device for determining whether the metal detection equipment might be malfunctioning or whether the inability of the equipment to locate the metal object sought for is actually due to the absence of metallic objects.
Also possible as an alternative to in-the-field testing is the use of the same or similar test apparatus at a dispatch point prior to the metal detection equipment being taken into the field for use. We have determined that the most frequent causes of metal detector malfunction are maladjustment and weakened batteries. Therefore, periodic dispatch point testing will obviate the majority of in-the-field equipment failures, while permitting one test device to be used to service many metal detectors.
Metal detector equipment malfunctions are of three basic types. The first type includes malfunctions in the receiver apparatus. The second type encompasses malfunctions in the transmitter apparatus. A third type involves those situations in which the transmitter and receiver are independently correctly functioning but fail to coact as intended such as, for example, when one of the units is misaligned or misadjusted. The invention disclosed herein is usable for detecting any and all of these conditions and for correcting some problems of the third type.